The invention relates to modifying the rigid substrate of a fixed abrasive article used in semiconductor wafer modification.
Chemical mechanical planarization (CMP) processes are used in semiconductor wafer fabrication to polish and planarize a semiconductor wafer. CMP processes involve placing an abrasive between a relatively stiff pad and a semiconductor wafer and moving the pad and the semiconductor wafer in relation to each other to modify the surface of the wafer. The abrasive used in a CMP process can be in the form of a slurry, i.e., a liquid medium that includes abrasive particles, or a fixed abrasive element, e.g., an element that includes abrasive particles bonded to a backing.
CMP processes attempt to remove material selectively from relatively higher locations, i.e., features having dimensions on the scale of those features commonly produced by photolithography, to planarize the wafer surface. CMP processes also attempt to remove material uniformly on the scale of the semiconductor wafer so that each die on the wafer is planarized to the same degree in an equivalent period of time. The rate of planarization for each die is preferably uniform over the entire wafer. It is difficult to achieve both of these objectives simultaneously because semiconductor wafers are often warped or curved. Some semiconductor wafers also include numerous step height variations or protrusions, which are produced during the fabrication sequence of an integrated circuit on a wafer. These height variations and the curvature and warp of the semiconductor wafer can interfere with the uniformity of the polishing process such that some regions of the wafer become over polished while other regions remain under polished.
CMP processes that employ a slurry have been modified in an effort to overcome the problem of non-uniform polishing. One such effort employs a composite polishing pad that includes a first layer of elastic material, which is attached to a polishing table, and a second layer of a stiff material covering the elastic layer. The second layer includes an array of tiles separated by channel regions. The channel regions channel slurry across the surface of the polishing pad during the polishing process. Other composite polishing pads include a third layer of a relatively low modulus spongy porous material that transports slurry across the surface of the wafer being polished. During polishing liquid can be transported through the porous material and into the lower layers of the polishing pad.
Fixed abrasive CMP processes do not rely on the transport of loose abrasive particles over the surface of the polishing pad to effect polishing. Instead, such processes use fixed abrasive polishing pads, which include a number of three-dimensional abrasive composites fixed in location on a backing. The three-dimensional abrasive composites include abrasive particles disposed in a binder and bonded to the backing, which forms a relatively high modulus fixed abrasive element. During the CMP process, the wafer surface is polished by contact with the fixed abrasive composites and a substantial majority of the abrasive particles in the abrasive composites remain bonded to the backing.
After a CMP polishing process the semiconductor wafer will have an edge exclusion zone, i.e., a zone at the edge of a polished semiconductor wafer that is not polished sufficiently to provide useful components, e.g., semiconductor components. The portion of the semiconductor wafer that constitutes the edge exclusion zone could be used to make semiconductor devices if it were uniform. Thus, the area of the edge exclusion zone affects the die yield of the wafer.
In one aspect, the invention features an abrasive article including a) a fixed abrasive element including a plurality of abrasive particles, b) a resilient element, and c) a plurality of rigid segments disposed between the fixed abrasive element and the resilient element.
In some embodiments the rigid segments are attached to one another. In other embodiments the rigid segments are detached from one another. In one embodiment the rigid segments extend from a common substrate and are at least partially defined by a plurality of intersecting grooves in the substrate.
In one embodiment the fixed abrasive element includes a discontinuous layer. In another embodiment the fixed abrasive element includes a plurality of fixed abrasive segments, each fixed abrasive segment being coextensive with one of the rigid segments. In some embodiments the fixed abrasive element extends continuously across a plurality of the rigid segments. In another embodiment the fixed abrasive element is bonded to the rigid segments. In other embodiments the rigid segments are bonded to the resilient element.
In another embodiment the resilient element includes a plurality of resilient segments. In some embodiments the resilient segments are bonded to the rigid segments.
In another embodiment the fixed abrasive element includes a textured, three-dimensional fixed abrasive element. In some embodiments the fixed abrasive element includes a plurality of three-dimensional fixed abrasive composites.
In some embodiments the rigid segments include a top surface, a side wall and a union between the top surface and the sidewall, wherein the union is beveled. In other embodiments the rigid segments include a top surface, a side wall and a union between the top surface and the side wall, wherein the union between the top surface and the sidewall is curved. Another embodiment includes rigid segments that interdigitate with one another.
In other embodiments the rigid segments define a shape selected from the group consisting of a circle, ellipse, triangle, square, rectangle, pentagon, hexagon, heptagon, and octagon. In some embodiments the rigid segments are selected from the group consisting of pyramidal, conical, cylindrical, frusto-conical, frusto-pyramidal and other frusta.
In other embodiments the rigid segments have a cross-sectional area taken in a plane of the segment that is parallel with the abrasive surface of no greater than 400 mm2.
In another aspect, the abrasive article includes a) a fixed abrasive element including i) a backing, ii) a composition disposed on a first major surface of the backing, the composition including a binder and a plurality of abrasive particles, and b) a rigid element bonded to a second major surface of the backing, the rigid element including a plurality of rigid segments.
In other aspects the abrasive article includes a fixed abrasive element including a plurality of abrasive particles, a resilient element and a plurality of rigid elements disposed between the fixed abrasive element and the resilient element, the abrasive article being capable of conforming to the curvature of the surface of a semiconductor wafer and being rigid relative to a die on the surface of a semiconductor wafer.
In one aspect the invention features an apparatus for modifying the surface of a semiconductor wafer, the apparatus including a fixed abrasive element including a plurality of abrasive particles, a resilient element and a plurality of rigid segments disposed between the fixed abrasive element and the resilient element. In one embodiment the fixed abrasive element includes a textured, three-dimensional, fixed abrasive element. In another embodiment the fixed abrasive element includes a three-dimensional fixed abrasive composites. In other embodiments the fixed abrasive element is bonded to the rigid segments. In some embodiments the rigid segments are bonded to the resilient element.
In one embodiment the fixed abrasive element is capable of moving relative to the rigid segments. In another embodiment the fixed abrasive element and the rigid segments are capable of moving relative to the resilient element. In other embodiments the apparatus further includes a first web including the fixed abrasive element, a second web including the plurality of rigid segments, and a third web including the resilient element.
In another embodiment the first web and the second web are movable relative to each other. In other embodiments the second web and the third web are movable relative to each other. In another embodiment the first web and the third web are movable relative to each other. In some embodiments the first web, the second web and the third web are movable relative to each other.
In some embodiments the apparatus further includes a web including a first region including a first plurality of rigid segments having a first cross-sectional area and a second region including a second plurality of rigid segments having a second cross-sectional area, the first cross-sectional area being different from the second cross-sectional area. In one embodiment the rigid layer includes a material selected from the group consisting of metal and plastic.
In other aspects the invention features a method of modifying the surface of a semiconductor wafer, the method including contacting an above-described abrasive article with a semiconductor wafer and moving the semiconductor wafer and the abrasive article relative to each other. In one embodiment the method further includes contacting a first region of the abrasive article with a semiconductor wafer, the first region including a first plurality of rigid segments having a first cross-sectional area, moving the semiconductor wafer and the fixed abrasive article relative to each other, contacting a second region of the abrasive article with the semiconductor wafer, the second region including a second plurality of the rigid segments having a second cross-sectional area and moving the semiconductor wafer and the fixed abrasive article relative to each other. In other embodiments the abrasive article further includes a web, the web including the plurality of rigid segments, the method further including indexing the web from a first position to a second position.
The term xe2x80x9cfixed abrasive articlexe2x80x9d refers to an abrasive article that is substantially free of unattached abrasive particles except as incidentally may be generated during the planarization process.
The term xe2x80x9cthree-dimensional abrasive articlexe2x80x9d refers to an abrasive article having numerous abrasive particles extending throughout at least a portion of its thickness such that removing some of the particles during planarization exposes additional abrasive particles capable of performing the planarization function.
The term xe2x80x9ctextured abrasive articlexe2x80x9d refers to an abrasive article having raised portions and recessed portions in which at least the raised portions contain abrasive particles and binder.
The term xe2x80x9cabrasive compositexe2x80x9d refers to a shaped body that includes abrasive particles and a binder.
The invention features an abrasive article that is able to substantially conform to the global topography of the surface of the wafer to be modified while maintaining uniform pressure on the wafer. The abrasive article is particularly well suited to producing semiconductor wafers that exhibit good surface uniformity. The presence of rigid segments in the subpad of the abrasive article provides an abrasive article that exhibits localized rigidity, i.e., the interaction between the abrasive article and the semiconductor wafer is rigid over an area that approximates the area of the rigid segment, which facilitates preferentially removing material from the wafer surface at points that are high relative to their surrounding area, i.e., an area that approximates the area of the rigid segment, while maintaining the global wafer-scale topography on the wafer surface. The abrasive article is also capable of polishing a semiconductor wafer so as to minimize the degree of edge exclusion present on the surface of the wafer, and maximize the useful region of the wafer.
The segmented rigid element, when combined with a fixed abrasive element, provides enhanced wafer uniformity while maintaining good planarization.
The segmented rigid element provides a mechanism for managing the competing requirements of local non-uniform material removal, which is necessary for planarization, and global uniform material removal, which is necessary for uniform processing of each die, including the die at the edge of the wafer.
Other features of the invention will be apparent from the following description of preferred embodiments thereof, and from the claims.